I just checked i think we cannot add mapping.vmdk file as it's type is a "File" and not a "Virtual Disk".
Basically it should work to just delete the RDM .vmdk files. There should be two files, the header/descriptor .vmdk file (a few hundred bytes in size) and the RDM .vmdk file which shows up with the LUN size. It's the header .vmdk file which has to be mapped to the VM.
Please post a screenshot of the Datastore Browser window, showing the files (with sizes, time stamps, ...) or - even better - post a list of files in the VM's folder by running ls -lisa from the command line.
André